From the first day of its discovery electrohydraulic effect has been and still remains a constant source of a number of innovative technological processes that are now widely used worldwide [1] in various industries. The use of electrohydraulic technology in oil production is also efficient. References [2-4] dealing with seismoacoustic technology show that low-frequency oscillations are beneficial to oil recovery. Electrohydraulic devices were first used within the seismic-acoustic technology in 1992.
The downhole devices diameter of current electrohydraulic equipment designed to work in oil and gas wells is 102 mm [5-8]. There is also a device with 69.9 mm in diameter and 11.8 m length [9]. Thus, due to their dimensions, these devices can only be operated through casing (capital string). At the same time, all existing methods of oil production (free-flow, gas-lift, pump) involve using of tubing.
Removing and running-in of the tubing is a fairly laborious process, other than time and cost it entails tubing resource (wire connections) reduction. In oil-wells where the pump oil recovery method is used the above-listed downhole devices can be used in the course of basic well servicing or total overhaul, when the tubing is removed anyway, and the work can be carried out through the casing. However, removing of the casing from wells with free-flow and gas-lift methods of oil production is inexpedient, especially in offshore wells. In that case it is appropriate to apply an electrohydraulic device with external diameter not exceeding 52 mm for stimulation of the oil reservoir. This provides the possibility of using it with almost all the existing tubings, because the most common tubings are those with a diameter of 60-89 mm.
A device consisting of a surface power source and a downhole device is also known [8]. The downhole device is made in the form of a hollow cylinder case divided with partitions into airtight sections, contains electrically interconnected charging apparatus, block of storage capacitors and a discharge unit with electrodes. The apparatus also has a commutation device mounted in its cavity, which is connected to a control board and a power source, and it operates automatically. The commutation device is in the same section as the block of storage capacitors, and the section where the block of storage capacitors and the commutation device are fixed is filled with electrically insulating medium. DC voltage is applied from the surface power source to the charging apparatus. The block of storage capacitors is charged to the required voltage value with capacitors being connected in parallel and then discharged, which ensures the supply of the output voltage to the electrodes of the discharge unit. After the charging of the block is over storage capacitors are switched to the serial connection. Then the block of storage capacitors is discharged providing an increase in its output voltage in stepped proportion to the number of capacitors. The DC voltage applied to the charger is set within the range of 300-150 V. The maximum value of the required voltage for charging the block of storage capacitors is taken equal to 20-27 kV.
Due to the use of complex electric circuit and to the need to charge the capacitors up to the voltage of 20-27 kV such downhole device has large dimensions—the diameter of 102 mm and the length not less than 2500 mm.
A device [6, 7] with all the necessary components and elements is known: energy storage units, electric ignition circuits, feeding unit for feeding metal wire to the working interelectrode space. The feeding unit consists of the housing, high-voltage electrode unit, low-voltage electrode unit in which there is a supply port for feeding the wire to the interelectrode space. The housing has the main part, the end part and jumpers connecting the parts specified above. The specified parts of the housing are formed as an integral unit. The high-voltage electrode unit is in the main part of the housing. The low-voltage electrode unit is in the end of the housing. The housing wall has a through hole going through the main part, the jumper and the end part. The hole is for the electrical wiring. The high-voltage electrode unit of the downhole source of seismic energy contains an electrode, two discs made of dielectric material, a bushing, a taper bushing. The low-voltage electrode unit of the downhole source of seismic energy contains a contact member, a toothed bushing with a tapered portion, and a guide tube.
Patents [6, 7] contain a detailed description of electrode design and no description of the operation of energy storage units, that of the electric ignition circuit and the wire feed unit. But judging by the fact that the above downhole devices have a diameter of 102 mm, all the proposed devices have large dimensions.
There is also known the borehole source of elastic vibrations [5] we took as the prototype, which consists of a downhole device with an energy storage unit, charging unit, discharger with ignition circuit, electropulse discharger with two electrodes, feeding unit for feeding metal wire to the working interelectrode space in it. The feeding unit consists of reel for the wire, and the tread drive. The wire drive is made in the form of two metal plates with one side of each of them fixed on the opposite sides of the bar. The opposite pointed sides of the plates are pressed by a spring to the wire on the guide platform and oriented at an angle thereto, the angle providing for the platform's rotary engagement and movement towards the interelectrode space with the reciprocal motion of the rod connected by an axis and pull lines to the movable armature of the solenoid. The rod and the pull lines connected to the armature of the solenoid are connected by an axis going through a hole in a dielectric plate. The downhole device has a relay. The discharge circuit of the storage capacitors of the downhole device has Rogowski coil.
The diameter of the downhole tool of the prototype under consideration is also 102 mm, which is due to the large dimensions of the wire feeding unit. The solenoid and additional equipment to enable it to work is used as a drive for pulling the wire, which reduces the reliability of the drive and the operation of the borehole tool in general.